Electrolyte compound additive, electrolyte and secondary battery

Abstract

The present invention discloses an electrolyte compound additive, an electrolyte, and a secondary battery. The electrolyte compound additive comprises an unsaturated sulfonate compound and a borate compound. The electrolyte compound additive of the present invention is used in secondary batteries, particularly sodium-ion batteries, and can balance high-temperature cycling performance with low-temperature discharge performance, achieving a wide operating temperature range of -40°C to 70°C.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to an electrolyte compound additive, an electrolyte and a secondary battery. Background Art

[0002] In recent years, secondary batteries have attracted widespread attention due to their high operating voltage, high specific energy, long cycle life and no memory effect. They have become the mainstream power batteries, and with the rapid development of the new energy field, the performance requirements for secondary batteries have become increasingly higher. In secondary batteries, the stability of the electrode material / electrolyte interface has a key influence on the cycle stability of the battery material. Electrolyte additives can fully contact with the electrode material in the battery and form a stable interface film on the surface of the electrode material during the charge and discharge process, thus becoming a convenient, effective and low-cost method to modify the electrode / electrolyte interface and improve the stability of the material. In addition, different electrolyte additives can adjust the composition and structure of the interface film, which has an important influence on the electrochemical performance and stability of the entire battery system. Especially for sodium ion batteries, due to the large radius of sodium ions, the transport activity is low and they are greatly affected by high and low temperatures, which places higher requirements on the electrolyte.

[0003] Patent CN 108963336 B combines the synergistic effects of silyl methanesulfonate and unsaturated phosphate additives to form a dense, stable, and compatible passivation film on the positive and negative surfaces of the battery, thereby improving the battery's high-temperature cycling, storage, and low-temperature performance. However, the invention's test temperature range is limited to -20 to 45°C. While a dense positive electrode passivation film improves high-temperature performance, it may exhibit greater impedance at lower temperatures, hindering low-temperature performance.

[0004] Patent CN 116826175 A uses chain sulfonate compounds and cyclic sultones as additives to promote the formation of a sulfur-containing SEI film, thereby improving high-temperature storage performance. The patent's solvent system contains a large amount of low-boiling-point substances, which can ensure good capacity retention at low temperatures while also ensuring high-temperature storage performance. However, it may be difficult to achieve long-term cycling at high temperatures.

[0005] It can be seen that most of the additives in the prior art only show excellent effects at high or low temperatures. Therefore, it is still necessary to study an electrolyte compound additive that can take into account both high and low temperature performance. Summary of the Invention

[0006] The present invention addresses the problems in the prior art and discloses an electrolyte compound additive for use in secondary batteries, especially sodium ion batteries, which can achieve both high-temperature cycle performance and low-temperature discharge performance.

[0007] The present invention is achieved through the following technical solutions:

[0008] In a first aspect, the present application provides an electrolyte compound additive, comprising an unsaturated sulfonate compound represented by structural formula I and a borate compound represented by structural formula II:

[0009]

[0010] In some embodiments, in the structural formula I, R1 and R2 are independently selected from one of hydrogen, halogen, nitrile, C1-C8 substituted or unsubstituted alkyl, C1-C8 substituted or unsubstituted alkoxy, C2-C8 substituted or unsubstituted unsaturated hydrocarbon, C6-C12 substituted or unsubstituted aryl, and at least one of R1 and R2 is selected from C2-C8 substituted or unsubstituted unsaturated hydrocarbon, wherein when R1 and R2 are substituted, the substituent is selected from C1-C4 alkyl, C1-C4 alkoxy, thiol, thioether, keto, one of an aldehyde group, an ester group, an ether group, an amine group, an imine group, an amide group, a nitro group, a carboxylic acid group, a carbonate group, an isocyanate group, a carbamate group, a halogen group, and a nitrile group; or, R1 and R2 together constitute a C3-C6 substituted or unsubstituted unsaturated cyclic hydrocarbon, wherein when R1 and R2 are substituted, the substituent is selected from one of a C1-C4 alkyl group, a C1-C4 alkoxy group, a thiol group, a sulfide group, a ketone group, an aldehyde group, an ester group, an ether group, an amine group, an imine group, an amide group, a nitro group, a carboxylic acid group, a carbonate group, an isocyanate group, a carbamate group, a halogen group, and a nitrile group;

[0011] In the structural formula II, A + Selected from Na + , K + 、Li + wherein R3 and R4 are independently selected from one of hydrogen, halogen, nitrile, C1-C8 substituted or unsubstituted alkyl, C1-C8 substituted or unsubstituted alkoxy, C2-C8 substituted or unsubstituted alkenyl, C2-C8 substituted or unsubstituted alkynyl, and C6-C12 substituted or unsubstituted aryl; wherein when R3 and R4 are substituted, the substituent is selected from one of C1-C4 alkyl, C1-C4 alkoxy, thiol, thioether, keto, aldehyde, ester, ether, amine, imine, amide, nitro, carboxylic acid, carbonate, isocyanate, carbamate, halogen, and nitrile.

[0012] The halogen mentioned in this application includes F, Cl, Br, and I, preferably F.

[0013] As a further embodiment, according to the structural characteristics of the unsaturated sulfonic acid ester compound (structural formula I), it can be divided into three categories: chain acyclic unsaturated sulfonic acid ester, chain unsaturated sulfonic acid ester containing aromatic ring, and unsaturated cyclic sulfonic acid ester. R1 and R2 are independently selected from one of hydrogen, halogen, nitrile, C1-C6 substituted or unsubstituted alkyl, C1-C6 substituted or unsubstituted alkoxy, C2-C6 substituted or unsubstituted unsaturated hydrocarbon, and C6-C10 substituted or unsubstituted aryl, and at least one of R1 and R2 is selected from C2-C6 substituted or unsubstituted unsaturated hydrocarbon, wherein when R1 and R2 are substituted, the substituent is selected from C1- one of a C2 alkyl group, a C1-C2 alkoxy group, a thiol group, a thioether group, a ketone group, an aldehyde group, an ester group, an ether group, an amine group, an imine group, an amide group, a nitro group, a carboxylic acid group, a carbonate group, an isocyanate group, a carbamate group, a halogen group, and a nitrile group; or, R1 and R2 together constitute a C3-C6 substituted or unsubstituted unsaturated cyclic hydrocarbon, wherein when R1 and R2 are substituted, the substituent is selected from one of a C1-C2 alkyl group, a C1-C2 alkoxy group, a thiol group, a thioether group, a ketone group, an aldehyde group, an ester group, an ether group, an amine group, an imine group, an amide group, a nitro group, a carboxylic acid group, a carbonate group, an isocyanate group, a carbamate group, a halogen group, and a nitrile group.

[0014] In the chain acyclic unsaturated sulfonic acid ester, as part of the preferred embodiment, R1 and R2 are independently selected from one of hydrogen, halogen, nitrile, C1-C4 substituted or unsubstituted alkyl, C1-C4 substituted or unsubstituted alkoxy, and C2-C4 substituted or unsubstituted unsaturated hydrocarbon, and at least one of R1 and R2 is selected from C2-C4 substituted or unsubstituted unsaturated hydrocarbon, wherein when R1 and R2 are substituted, the substituent is selected from one of C1-C2 alkyl, C1-C2 alkoxy, amine, imine, nitro, isocyanate, carbamate, halogen, and nitrile.

[0015] In the above structure, the chain acyclic unsaturated sulfonic acid ester includes a single-sided chain acyclic unsaturated sulfonic acid ester and a double-sided chain acyclic unsaturated sulfonic acid ester; wherein, single-sided and double-sided refer to whether the unsaturated group is located on one side of the sulfonic acid ester group or on both sides of the sulfonic acid ester group.

[0016] In the unilateral acyclic unsaturated sulfonic acid ester, as a preferred embodiment, R1 is selected from one of hydrogen, halogen, nitrile, and C1-C4 substituted or unsubstituted alkyl groups, and R2 is selected from one of C2-C4 substituted or unsubstituted unsaturated hydrocarbon groups, wherein when R1 and R2 are substituted, the substituent is selected from one of halogen and nitrile groups.

[0017] In the double-side chain acyclic unsaturated sulfonic acid ester, as a preferred embodiment, R1 and R2 are both selected from C2-C4 substituted or unsubstituted unsaturated hydrocarbon groups, wherein when R1 and R2 are substituted, the substituent is selected from one of halogen and nitrile groups.

[0018] Furthermore, the chain acyclic unsaturated sulfonic acid ester is preferably one of the chain acyclic unsaturated sulfonic acid esters terminated by an unsaturated bond (the unsaturated bond is located at the end of R1 or R2), specifically a single-sided chain acyclic unsaturated sulfonic acid ester terminated by an unsaturated bond and a double-sided chain acyclic unsaturated sulfonic acid ester terminated by an unsaturated bond.

[0019] The chain-like unsaturated sulfonic acid ester containing an aromatic ring can be divided into two types of compounds represented by structural formula III and structural formula IV according to their structural characteristics;

[0020]

[0021] In the structural formula III, R5 is selected from one of hydrogen, halogen, nitrile, and C1-C4 substituted or unsubstituted alkyl groups, and R6 is selected from one of C2-C4 substituted or unsubstituted unsaturated hydrocarbon groups, wherein when R5 and R6 are substituted, the substituent is selected from one of C1-C2 alkyl groups, C1-C2 alkoxy groups, amino groups, imine groups, nitro groups, isocyanate groups, carbamate groups, halogen groups, and nitrile groups.

[0022] Furthermore, in the structural formula III, R5 is selected from one of hydrogen, halogen, nitrile, and C1-C2 substituted or unsubstituted alkyl, and R6 is selected from one of C2-C4 substituted or unsubstituted unsaturated hydrocarbon groups, wherein when R5 and R6 are substituted, the substituent is selected from one of C1-C2 alkyl, halogen, and nitrile.

[0023] In the structural formula IV, R7 is selected from a C2-C4 substituted or unsubstituted unsaturated hydrocarbon group, and R8 is selected from one of hydrogen, halogen, nitrile group, and C1-C4 substituted or unsubstituted alkyl group, wherein when R7 and R8 are substituted, the substituent is selected from one of a C1-C2 alkyl group, a C1-C2 alkoxy group, an amine group, an imine group, a nitro group, an isocyanate group, a carbamate group, a halogen group, and a nitrile group.

[0024] Furthermore, in the structural formula IV, R7 is selected from a C2-C4 substituted or unsubstituted unsaturated hydrocarbon group, and R8 is selected from one of hydrogen, halogen, nitrile, and C1-C2 substituted or unsubstituted alkyl groups, wherein when R7 and R8 are substituted, the substituent is selected from one of C1-C2 alkyl groups, halogen, and nitrile groups.

[0025] Compared with the chain-like unsaturated sulfonic acid ester containing an aromatic ring shown in structural formula IV, the benzenesulfonic acid ester group in the chain-like unsaturated sulfonic acid ester containing an aromatic ring shown in structural formula III can enhance the reactivity of the unsaturated bond in R6, which is beneficial to participating in the film-forming reaction of the electrode material, thereby significantly improving the high and low temperature performance of the battery.

[0026] In the unsaturated cyclic sulfonate, R1 and R2 together constitute a C3-C6 substituted or unsubstituted unsaturated cyclic hydrocarbon, wherein when R1 and R2 are substituted, the substituent is selected from one of a C1-C2 alkyl group, a C1-C2 alkoxy group, an amine group, an imine group, a nitro group, an isocyanate group, a carbamate group, a halogen group, and a nitrile group.

[0027] Furthermore, R1 and R2 together constitute a C3-C6 substituted or unsubstituted unsaturated cyclic hydrocarbon, wherein when R1 and R2 are substituted, the substituent is selected from one of halogen and nitrile.

[0028] As examples of some specific unsaturated sulfonic acid ester compounds, the following compounds are given:

[0029]

[0030] Among them, compounds 1-1 to 1-3 are chain acyclic unsaturated sulfonic acid esters, compound 1-1 is a single-sided chain acyclic unsaturated sulfonic acid ester terminated by an unsaturated bond, compounds 1-2 and 1-3 are double-sided chain acyclic unsaturated sulfonic acid esters, compound 1-3 is a double-sided chain acyclic unsaturated sulfonic acid ester terminated by an unsaturated bond, compounds 1-4 to 1-11 are chain unsaturated sulfonic acid esters containing aromatic rings, compounds 1-4 to 1-10 are chain unsaturated sulfonic acid esters containing aromatic rings as shown in structural formula III, compound 1-11 is a chain unsaturated sulfonic acid ester containing aromatic rings as shown in structural formula IV, and compound 1-12 is an unsaturated cyclic sulfonic acid ester.

[0031] As a further solution, in the structural formula II, A + Selected from Na + , K + 、Li + R3 and R4 are independently selected from one of hydrogen, halogen, nitrile, C1-C4 substituted or unsubstituted alkyl, C1-C4 substituted or unsubstituted alkoxy, C2-C4 substituted or unsubstituted alkenyl, C2-C4 substituted or unsubstituted alkynyl, and C6-C8 substituted or unsubstituted aryl, wherein when R3 and R4 are substituted, the substituent is selected from one of C1-C2 alkyl, C1-C2 alkoxy, amino, imino, nitro, isocyanate, carbamate, halogen, and nitrile.

[0032] Furthermore, in the structural formula II, A + Selected from Na + , K+ 、Li + R3 and R4 are independently selected from one of hydrogen, halogen, nitrile, C1-C4 substituted or unsubstituted alkyl, C2-C4 substituted or unsubstituted alkenyl, C2-C4 substituted or unsubstituted alkynyl, wherein when R3 and R4 are substituted, the substituent is selected from halogen or nitrile.

[0033] Furthermore, in the structural formula II, A + Selected from Na + , K + 、Li + R3 and R4 are independently selected from F or C1-C4 fluoroalkyl.

[0034] As examples of some specific borate compounds, the following compounds are given:

[0035]

[0036] Unsaturated sulfonate compounds and borate compounds can form a uniform, dense interfacial film at the electrode / electrolyte interface of secondary batteries, reducing side reactions between the electrolyte and the electrode material and significantly improving the battery's high-temperature cycling performance. Both additives contain sulfonate groups, which can effectively participate in the film-forming reaction on the electrode material surface, reducing interfacial impedance and achieving good low-temperature discharge performance. The presence of carbon double or triple bonds in unsaturated sulfonate compounds allows them to preferentially participate in film formation, while some borate compounds retain their ionic structure, enhancing the conductivity of the SEI film. The combined action of these two electrolyte additives can achieve a balanced performance of secondary batteries at both high and low temperatures.

[0037] In a second aspect, the present application provides an electrolyte comprising an organic solvent, a sodium salt and an additive, wherein the additive is the electrolyte compound additive provided in the first aspect of the present application.

[0038] In some embodiments, the total weight ratio of the additive in the electrolyte is 0.4-6 wt %, wherein the weight ratio of the unsaturated sulfonate compound to the borate compound is 1:(0.3-4).

[0039] Preferably, the unsaturated sulfonate compound accounts for 0.3-0.8 wt% of the electrolyte by weight. Excessive addition may increase electrolyte viscosity and reduce conductivity. It may also induce cross-linking between carbon double bonds in the unsaturated sulfonate, increasing film formation resistance and hindering ion transport efficiency between the positive and negative electrode surfaces, leading to deteriorated battery performance. Excessive addition may result in poor film formation, fail to improve interfacial stability, and hinder high- and low-temperature performance.

[0040] Preferably, the borate compound accounts for 1.0-1.5 wt% of the electrolyte by weight. Excessive additions may increase electrolyte viscosity, reduce conductivity, and create a thick and dense SEI film, hindering the normal ion insertion and extraction process and hindering the battery's low-temperature capacity. Excessive additions may result in an unstable SEI film formed with the unsaturated sulfonate compound, impairing the battery's high-temperature cycling stability.

[0041] Preferably, the mass ratio of the unsaturated sulfonate compound to the borate compound is 1:(2.5-3.5). Within this mass ratio range, the two electrolyte additives can better exert a synergistic effect, forming a uniform and dense interfacial film at the secondary battery electrode / electrolyte interface, reducing side reactions between the electrolyte and the electrode material. They also effectively participate in the film-forming reaction on the electrode material surface, reducing interfacial impedance, and achieving a balanced high and low temperature performance of the secondary battery.

[0042] In some embodiments, the organic solvent includes a carboxylate solvent and a carbonate solvent.

[0043] In some embodiments, the carboxylate solvent is selected from alkyl carboxylates or fluorocarboxylates. The alkyl carboxylates are selected from at least one of n-propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, ethyl propionate, propyl propionate, butyl propionate, isobutyl propionate, ethyl n-butyrate, and ethyl isobutyrate. The fluorocarboxylates are selected from at least one of ethyl fluoroacetate, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, 2,2,2-trifluoroethyl difluoroacetate, methyl pentafluoropropionate, and 2,2-difluoroethyl acetate.

[0044] In some embodiments, the carbonate solvent is selected from cyclic carbonate or chain carbonate. The cyclic carbonate is selected from at least one of ethylene carbonate, vinylene carbonate, fluoroethylene carbonate, propylene carbonate, and γ-butyrolactone. The chain carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, and dioctyl carbonate.

[0045] In some embodiments, the mass proportion of the carboxylate solvent in the electrolyte is 20-80 wt %, and the mass proportion of the carbonate solvent in the electrolyte is 10-75 wt %.

[0046] In some embodiments, the electrolyte salt is selected from at least one of sodium salt, potassium salt, and lithium salt.

[0047] In some embodiments, the sodium salt is selected from at least one of sodium dihydrogen phosphate, sodium phosphate, sodium carbonate, sodium nitrate, sodium perchlorate, sodium hydroxide, sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(trifluoromethylsulfonyl)imide, sodium dioxalatoborate, sodium difluorooxalatoborate, sodium difluorophosphate, and sodium difluorodioxalatophosphate.

[0048] In some embodiments, the potassium salt is selected from at least one of potassium fluoride, potassium carbonate, potassium phosphate, potassium hexafluorophosphate, potassium perchlorate, potassium trifluoromethanesulfonate, potassium bis(difluorosulfonyl)imide, potassium bis(oxalatoborate), potassium difluorooxalatoborate, and potassium bis(trifluoromethanesulfonyl)imide.

[0049] In some embodiments, the lithium salt is selected from at least one of lithium perchlorate, lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethylsulfonate, lithium difluorooxalatoborate, and lithium bis(oxalatoborate).

[0050] In some embodiments, the concentration of the electrolyte salt in the electrolyte is 0.3-2 mol / L.

[0051] Through the coordination of the above-mentioned component contents and the synergistic effect between the components, the electrolyte compound additive of the present invention can efficiently participate in the film-forming reaction on the surface of the electrode material, reduce the internal resistance of the secondary battery, and at the same time improve the film-forming stability of the electrode / electrolyte interface film and reduce the side reactions between the electrolyte and the electrode material. Therefore, it can simultaneously improve the high-temperature and low-temperature performance of the secondary battery, achieving both high and low-temperature performance.

[0052] In a third aspect, the present application provides a secondary battery selected from a lithium-ion battery, a sodium-ion battery, a potassium-ion battery, a nickel-cadmium battery, a nickel-hydrogen battery, a lead-acid battery, and a zinc-manganese battery, wherein the secondary battery comprises a positive electrode, a negative electrode, and the electrolyte provided in the second aspect of the present application.

[0053] Taking a sodium-ion battery as an example, the positive electrode includes a positive electrode current collector and a positive electrode material layer formed on the positive electrode current collector. The specific material of the positive electrode current collector is not particularly limited. As some specific examples, the positive electrode current collector is selected from aluminum foil. The positive electrode material layer includes a positive electrode active material. The specific type of positive electrode active material is not particularly limited. As some specific examples, the positive electrode active material is selected from one of sodium copper iron manganate, sodium nickel iron manganate, sodium vanadium phosphate, sodium vanadium fluorophosphate, sodium ferric pyrophosphate, sodium ferric sulfate, and modified sodium ferrocyanide.

[0054] In some embodiments, the negative electrode is a negative electrode current collector or a negative electrode current collector coated with a conductive layer, preferably a negative electrode current collector coated with a conductive layer. The specific material of the negative electrode current collector is not particularly limited. As some specific examples, the negative electrode current collector includes at least one of aluminum foil and copper foil. The conductive layer includes a conductive agent. The specific type of the conductive agent is not particularly limited. As some specific examples, the conductive agent includes at least one of soft carbon, hard carbon, ammonium titanate, metallic sodium, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0055] The characteristics and beneficial effects of the present invention are:

[0056] The composite electrolyte additives of the present invention, unsaturated sulfonate compounds and borate compounds, can form a uniform and dense interfacial film at the electrode / electrolyte interface of a secondary battery, reducing side reactions between the electrolyte and the electrode material and significantly improving the battery's high-temperature cycling performance. Simultaneously, both additives contain sulfonate groups, which can effectively participate in the film-forming reaction on the electrode material surface, reducing interfacial impedance and achieving good low-temperature discharge performance. The presence of carbon double or triple bonds in the unsaturated sulfonate compounds allows them to preferentially participate in film formation, while some borate compounds retain their ionic structure, enhancing the conductivity of the SEI film. The combined action of the two electrolyte additives can achieve a balanced high and low-temperature performance in secondary batteries, particularly sodium-ion batteries. DETAILED DESCRIPTION

[0057] In order to facilitate understanding of the present invention, the present invention will be described in more detail below, and embodiments of the present invention are given, but the scope of the present invention is not limited thereby.

[0058] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as commonly understood by technicians in the technical field to which this application belongs; the terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the description and claims of this application and any variations thereof are intended to cover non-exclusive inclusions.

[0059] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0060] In the description of the present application, the term "plurality" refers to two or more (including two), and "at least one" refers to one or more (including one, two, three, etc.).

[0061] Example 1

[0062] The electrolyte was prepared in an inert atmosphere glove box, with H2O and O2 contents both below 0.1 ppm. Diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propyl propionate, and ethyl butyrate were thoroughly mixed in a ratio of 2:2:1:3:2. Sodium hexafluorophosphate was added at a concentration of 1 mol / L. After complete dissolution, 0.5 wt% of compound 1-1 and 0.5 wt% of compound 2-1 were added.

[0063] Examples 2-12 and Comparative Examples 1-8:

[0064] The only difference from Example 1 is the additives. The specific formula is shown in Table 1, and the preparation steps are the same as Example 1.

[0065] Table 1 Composition and dosage of additives in comparative examples

[0066]

[0067] manual

[0068]

[0069] The sodium ion batteries prepared in Examples 1-12 and Comparative Examples 1-8 were subjected to performance tests respectively.

[0070] The positive electrode material Na 0.9 [Cu 0.22 Fe 0.3 Mn 0.48 ]O2, binder polyvinylidene fluoride (PVDF), and conductive agent conductive carbon black (SP) are mixed in a mass ratio of 94:3:3 and evenly coated on aluminum foil. After drying, the mixture is rolled and die-cut to obtain a positive electrode sheet; the negative electrode material hard carbon, thickener carboxymethyl cellulose (CMC), binder styrene butadiene rubber (SBR), and conductive agent conductive carbon black (SP) are mixed in a mass ratio of 93:2.5:3:1.5 and evenly coated on aluminum foil. After drying, the mixture is rolled and die-cut to obtain a negative electrode sheet. The positive and negative electrode sheets and the polypropylene separator are stacked in order, fixed with tape, and packaged after cold pressing. In a glove box with a dew point below -40°C, the electrolytes prepared in Examples 1-12 and Comparative Examples 1-8 are respectively injected into the battery cells. After standing at high temperature for 24 hours and standing at room temperature for 12 hours, the cells are formed, sealed, and capacity divided to produce a sodium ion battery with a theoretical capacity of 1500mAh. The normal temperature cycle test and high temperature cycle test are respectively carried out. The test conditions are as follows:

[0071] (1) High temperature cycle test: The sodium ion battery is placed in a 70°C environment, charged to 4.0V at a constant current and constant voltage of 1C, and then discharged to 1.5V at a constant current of 1C. The capacity retention rate is calculated based on the discharge capacity of the first cycle.

[0072] (2) Low temperature discharge test: The sodium ion battery was placed in a 25°C environment and charged to 4.0V at a constant current and constant voltage of 1C. Then, it was discharged to 1.5V at a constant current of 1C. Then, it was charged to 4.0V at a constant current and constant voltage of 1C. The discharge capacity obtained was used as the basis for calculating the capacity retention rate. The battery temperature after charging was lowered to -40°C and discharged to 1.5V at a constant current of 0.2C.

[0073] The test results are shown in Table 2.

[0074] Table 2 Sodium ion battery performance test results

[0075]

[0076] A comparison of the data results of Examples 1-12 and Comparative Examples 1-3 verifies that the addition of unsaturated sulfonate compounds and borate compounds to the electrolyte can significantly improve the high-temperature cycle performance and low-temperature discharge performance of the secondary battery, and the improvement effect after the combined use of the two is better than that of using unsaturated sulfonate compounds or borate compounds alone.

[0077] Comparison of the data from Examples 1-12 and Comparative Examples 4-5 demonstrates that, compared to ethyl methanesulfonate and ethyl benzenesulfonate, unsaturated sulfonate compounds containing carbon double or triple bonds preferentially participate in film formation, while some borate compounds retain their ionic structure, enhancing the conductivity of the SEI film. Their combined use can form a uniform, dense interface film on the electrode surface, thereby improving the high-temperature cycling and low-temperature discharge performance of the secondary battery.

[0078] A comparison of the data results of Examples 1-12 and Comparative Example 6 can verify that the borate compound of the present application has a cyclic structure with symmetrically distributed disulfonate groups on the ring. Compared with sodium difluorooxalate borate, the film formation impedance is smaller and the effect of improving high-temperature cycle performance and low-temperature discharge performance is more obvious.

[0079] Comparison of the data results of Examples 3, 8-12, and Comparative Examples 7-8 demonstrates that the additive mass ratio within the range of this application can significantly improve the high-temperature cycling performance and low-temperature discharge performance of the battery. However, excessive additive amounts may increase electrolyte viscosity, reduce conductivity, and increase film formation resistance, hindering ion transport efficiency between the positive and negative electrode surfaces and deteriorating battery performance. Excessive additive amounts can lead to poor film formation, fail to improve interfacial stability, and hinder improvements in high and low-temperature performance.

[0080] Comparison of the data results in Example 3 and Examples 6-7 demonstrates that borate compounds with nitrile groups as substituents can further improve the battery's high-temperature cycling performance compared to halogen substituents, but are detrimental to low-temperature discharge performance. This is because the nitrile group complexes with transition metals, inhibiting their dissolution. However, the nitrile group has a higher film-forming impedance, which is detrimental to the battery's low-temperature discharge. When the borate compound substituent is a halogen, combining it with an unsaturated sulfonate compound as an additive significantly improves the battery's high- and low-temperature performance. Therefore, F or a fluoroalkyl group is the optimal borate compound substituent.

[0081] Comparison of the data results in Examples 1-5 demonstrates that among the unsaturated sulfonate compounds, the chain-type aromatic-ring-containing unsaturated sulfonate (Compound 1-4) shown in Structural Formula III exhibits the best battery performance enhancement. The benzenesulfonate group in Compound 1-4 enhances the reactivity of the unsaturated bond, facilitating its participation in the film-forming reaction of the electrode material, thereby significantly improving the battery's high and low temperature performance. The unsaturated cyclic sulfonate (Compound 1-12) exhibits a weaker battery performance enhancement than Compound 1-4, presumably due to the higher reactivity of the unsaturated bond in the benzenesulfonate group than in the cyclic structure. Among the chain-type acyclic unsaturated sulfonates, the double-sided chain-type acyclic unsaturated sulfonate (Compound 1-3) terminated with bilateral unsaturated bonds exhibits the best battery performance enhancement. The unsaturated bond is more reactive at the end, and thus exhibits a battery performance enhancement effect closest to that of the chain-type aromatic-ring-containing unsaturated sulfonate (Compound 1-4) shown in Structural Formula III.

[0082] A comparison of the data results of Example 3, Example 8 and Example 9 can verify that: as the amount of unsaturated sulfonic acid ester compound added increases, the high-temperature cycle performance of the secondary battery gradually improves, but when the concentration of compound 1-3 is 1.0wt%, it may cause the carbon double bonds to form a cross-linked network, increase the interfacial impedance and thus inhibit the low-temperature discharge performance. Therefore, the mass proportion of the unsaturated sulfonic acid ester compound in the electrolyte of this application is preferably 0.3-0.8wt%.

[0083] A comparison of the data results of Example 3 and Examples 10-12 can verify that: as the amount of borate compound added increases, a more stable SEI film is formed on the surface of the positive and negative electrode materials, so that the high-temperature cycle performance and low-temperature discharge performance of the secondary battery are gradually improved. Therefore, the mass proportion of the borate compound in the electrolyte of the present application is preferably 1.0-1.5wt%.

[0084] A comparison of the data results of Example 3 and Examples 8-12 can verify that when the mass ratio of the unsaturated sulfonate compound to the borate compound is 1: (2.5-3.5), the effect of improving the high and low temperature performance of the battery is better. The two electrolyte additives can better play a synergistic role within this mass ratio range, forming a uniform and dense interface film at the secondary battery electrode / electrolyte interface, reducing the side reaction between the electrolyte and the electrode material, and jointly and efficiently participating in the film-forming reaction on the surface of the electrode material, reducing the interfacial impedance, and achieving a balance between the high and low temperature performance of the secondary battery.

[0085] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An electrolyte compound additive, characterized in that: The unsaturated sulfonate compound comprises an unsaturated sulfonate ester and a borate compound. The unsaturated sulfonate ester comprises a chain acyclic unsaturated sulfonate ester, a chain unsaturated sulfonate ester containing an aromatic ring, or an unsaturated cyclic sulfonate ester. The chain acyclic unsaturated sulfonate ester or the chain unsaturated sulfonate ester containing an aromatic ring has a structure shown in structural formula I, and the borate compound has a structure shown in structural formula II: ， Structural Formula Ⅰ ， Structural Formula II In the structural formula I, R1 and R2 are independently selected from one of hydrogen, halogen, nitrile, C1-C8 substituted or unsubstituted alkyl, C1-C8 substituted or unsubstituted alkoxy, C2-C8 substituted or unsubstituted unsaturated hydrocarbon, and C6-C12 substituted or unsubstituted aryl, and at least one of R1 and R2 is selected from one of C2-C8 substituted or unsubstituted unsaturated hydrocarbon, wherein the substituents of R1 and R2 when substituted are selected from one of C1-C4 alkyl, C1-C4 alkoxy, halogen, and nitrile; The unsaturated cyclic sulfonate has R1 and R2 together forming a C3-C6 substituted or unsubstituted unsaturated cyclic hydrocarbon, wherein when R1 and R2 are substituted, the substituent is selected from one of a C1-C4 alkyl group, a C1-C4 alkoxy group, a halogen group, and a nitrile group; In the structural formula II, A + Selected from Na + , K + 、Li + R3 and R4 are independently selected from one of hydrogen, halogen, nitrile, C1-C8 substituted or unsubstituted alkyl, C1-C8 substituted or unsubstituted alkoxy, C2-C8 substituted or unsubstituted alkenyl, C2-C8 substituted or unsubstituted alkynyl, and C6-C12 substituted or unsubstituted aryl, wherein when R3 and R4 are substituted, the substituent is selected from one of C1-C4 alkyl, C1-C4 alkoxy, halogen, and nitrile; In the electrolyte compound additive, the mass ratio of the unsaturated sulfonate compound to the borate compound is 1:(0.3-4).

2. The electrolyte compound additive according to claim 1, characterized in that: In the structural formula I, R1 and R2 are independently selected from one of hydrogen, halogen, nitrile, C1-C6 substituted or unsubstituted alkyl, C1-C6 substituted or unsubstituted alkoxy, C2-C6 substituted or unsubstituted unsaturated hydrocarbon, and C6-C10 substituted or unsubstituted aryl, and at least one of R1 and R2 is selected from one of C2-C6 substituted or unsubstituted unsaturated hydrocarbon, wherein when R1 and R2 are substituted, the substituent is selected from one of C1-C2 alkyl, C1-C2 alkoxy, halogen, and nitrile; The unsaturated cyclic sulfonic acid ester has a C3-C6 substituted or unsubstituted unsaturated cyclic hydrocarbon, and when substituted, the substituent is selected from one of a C1-C2 alkyl group, a C1-C2 alkoxy halogen group, and a nitrile group.

3. The electrolyte compound additive according to claim 1, characterized in that: The chain acyclic unsaturated sulfonic acid ester has a structure shown in structural formula I, wherein R1 and R2 are independently selected from one of hydrogen, halogen, nitrile, C1-C4 substituted or unsubstituted alkyl, C1-C4 substituted or unsubstituted alkoxy, and C2-C4 substituted or unsubstituted unsaturated hydrocarbon, and at least one of R1 and R2 is selected from a C2-C4 substituted or unsubstituted unsaturated hydrocarbon group, wherein when R1 and R2 are substituted, the substituent is selected from one of C1-C2 alkyl, C1-C2 alkoxy, halogen, and nitrile.

4. The electrolyte compound additive according to claim 1, characterized in that: The chain acyclic unsaturated sulfonic acid ester includes a single-side chain acyclic unsaturated sulfonic acid ester and a double-side chain acyclic unsaturated sulfonic acid ester; In the unilateral chain acyclic unsaturated sulfonic acid ester, R1 is selected from one of hydrogen, halogen, nitrile, and C1-C4 substituted or unsubstituted alkyl, and R2 is selected from one of C2-C4 substituted or unsubstituted unsaturated hydrocarbon groups, wherein when R1 and R2 are substituted, the substituent is selected from one of halogen and nitrile; In the double-side chain acyclic unsaturated sulfonic acid ester, R1 and R2 are both selected from C2-C4 substituted or unsubstituted unsaturated hydrocarbon groups, wherein when R1 and R2 are substituted, the substituent is selected from one of halogen and nitrile groups.

5. The electrolyte compound additive according to claim 1, characterized in that: The chain acyclic unsaturated sulfonic acid ester is a type of chain acyclic unsaturated sulfonic acid ester terminated with an unsaturated bond.

6. The electrolyte compound additive according to claim 4, characterized in that: The chain acyclic unsaturated sulfonic acid ester is a single-side chain acyclic unsaturated sulfonic acid ester terminated by an unsaturated bond and a double-side chain acyclic unsaturated sulfonic acid ester terminated by an unsaturated bond.

7. The electrolyte compound additive according to claim 1, characterized in that: The chain-like unsaturated sulfonic acid ester containing an aromatic ring includes two types of compounds represented by structural formula III and structural formula IV: ， Structural Formula III ， Structural Formula IV In the structural formula III, R5 is selected from one of hydrogen, halogen, nitrile, and C1-C4 substituted or unsubstituted alkyl, and R6 is selected from one of C2-C4 substituted or unsubstituted unsaturated hydrocarbon groups, wherein when R5 and R6 are substituted, the substituent is selected from one of C1-C2 alkyl, C1-C2 alkoxy, halogen, and nitrile; In the structural formula IV, R7 is selected from a C2-C4 substituted or unsubstituted unsaturated hydrocarbon group, and R8 is selected from one of hydrogen, halogen, nitrile, and C1-C4 substituted or unsubstituted alkyl groups, wherein when R7 and R8 are substituted, the substituent is selected from one of a C1-C2 alkyl group, a C1-C2 alkoxy group, halogen, and nitrile group.

8. The electrolyte compound additive according to claim 7, characterized in that: In the structural formula III, R5 is selected from one of hydrogen, halogen, nitrile, and C1-C2 substituted or unsubstituted alkyl, and R6 is selected from one of C2-C4 substituted or unsubstituted unsaturated hydrocarbon groups, wherein when R5 and R6 are substituted, the substituent is selected from one of C1-C2 alkyl, halogen, and nitrile; In the structural formula IV, R7 is selected from a C2-C4 substituted or unsubstituted unsaturated hydrocarbon group, and R8 is selected from one of hydrogen, halogen, nitrile, and C1-C2 substituted or unsubstituted alkyl groups, wherein when R7 and R8 are substituted, the substituent is selected from one of C1-C2 alkyl groups, halogen, and nitrile groups.

9. The electrolyte compound additive according to claim 1, characterized in that: In the structural formula II, A + Selected from Na + , K + 、Li + R3 and R4 are independently selected from one of hydrogen, halogen, nitrile, C1-C4 substituted or unsubstituted alkyl, C1-C4 substituted or unsubstituted alkoxy, C2-C4 substituted or unsubstituted alkenyl, C2-C4 substituted or unsubstituted alkynyl, C6-C8 substituted or unsubstituted aryl, wherein when R3 and R4 are substituted, the substituent is selected from one of C1-C2 alkyl, C1-C2 alkoxy, halogen and nitrile.

10. The electrolyte compound additive according to claim 1, characterized in that: In the structural formula II, A + Selected from Na + , K + 、Li + R3 and R4 are independently selected from one of hydrogen, halogen, nitrile, C1-C4 substituted or unsubstituted alkyl, C2-C4 substituted or unsubstituted alkenyl, C2-C4 substituted or unsubstituted alkynyl, wherein when R3 and R4 are substituted, the substituent is selected from halogen or nitrile.

11. The electrolyte compound additive according to claim 1, characterized in that: In the structural formula II, A + Selected from Na + , K + 、Li + R3 and R4 are independently selected from F or C1-C4 fluoroalkyl.

12. An electrolyte, characterized in that: The invention comprises an organic solvent, an electrolyte salt and the electrolyte compound additive according to any one of claims 1 to 11.

13. The electrolyte according to claim 12, characterized in that The organic solvent includes carboxylate solvents and carbonate solvents; The carboxylate solvent is selected from alkyl carboxylates or fluorocarboxylates, wherein the alkyl carboxylates are selected from at least one of n-propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, ethyl propionate, propyl propionate, butyl propionate, ethyl n-butyrate, and ethyl isobutyrate, and the fluorocarboxylates are selected from at least one of ethyl fluoroacetate, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, 2,2,2-trifluoroethyl difluoroacetate, methyl pentafluoropropionate, and 2,2-difluoroethyl acetate; The carbonate solvent is selected from cyclic carbonate or chain carbonate, wherein the cyclic carbonate is selected from at least one of ethylene carbonate, vinylene carbonate, fluoroethylene carbonate, propylene carbonate, and γ-butyrolactone, and the chain carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, and dioctyl carbonate; The electrolyte salt is selected from at least one of sodium salt, potassium salt and lithium salt; The sodium salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(trifluoromethylsulfonyl)imide, sodium dioxalatoborate, sodium difluorooxalatoborate, sodium difluorophosphate, and sodium difluorodioxalatophosphate; The potassium salt is selected from at least one of potassium hexafluorophosphate, potassium perchlorate, potassium trifluoromethanesulfonate, potassium difluorophosphate, potassium bisdifluorosulfonyl imide, potassium bisoxalatoborate, potassium difluorooxalatoborate, potassium bistrifluoromethanesulfonyl imide, and potassium tetrafluorooxalatophosphate; The lithium salt is selected from at least one of lithium perchlorate, lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethylsulfonate, lithium difluorooxalatoborate, and lithium bis(oxalatoborate).

14. The electrolyte according to claim 12, characterized in that The total weight of the electrolyte compound additive in the electrolyte accounts for 0.4-6wt%.

15. The electrolyte according to claim 12, characterized in that The mass ratio of the unsaturated sulfonate compound in the electrolyte is 0.3-0.8wt%, the mass ratio of the borate compound in the electrolyte is 1.0-1.5wt%, and the mass ratio of the unsaturated sulfonate compound to the borate compound is 1:(2.5-3.5).

16. The electrolyte according to claim 13, characterized in that The mass proportion of the carboxylate solvent in the electrolyte is 20-80wt%, and the mass proportion of the carbonate solvent in the electrolyte is 10-75wt%; The concentration of the electrolyte salt in the electrolyte is 0.3-2 mol / L.

17. A secondary battery, characterized in that: The secondary battery comprises a positive electrode, a negative electrode and the electrolyte according to any one of claims 12 to 16, wherein the secondary battery is selected from one of a lithium ion battery, a sodium ion battery and a potassium ion battery.

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